Why does my 1 TB disk show 931 GB?
File size converter: bytes, KB, MB, GB, TB. Shows two systems side-by-side: decimal (1 KB = 1000 B, used by disk makers and networking) and binary (1 KiB = 1024 B, used by RAM and Windows).
That's exactly why a disk advertised as "1 TB" shows "931 GB" in your computer. Same number of bytes, counted differently.
How to use it
- Type a value and pick a unit (e.g. GB or GiB).
- The left table shows decimal (KB, MB, GB, TB, ×1000 between levels).
- The right table shows binary (KiB, MiB, GiB, TiB, ×1024 between levels).
- The same numbers are NOT in both columns. 1 GB ≠ 1 GiB. 1 GB = 1 billion bytes, 1 GiB = 1.074 billion bytes.
When this is useful
The most common uses:
- Buying a disk. Bought a "2 TB" SSD, the system shows "1.81 TB". That's NOT a scam: the manufacturer used decimal, the system used binary.
- Internet plan. "1 Gbps" is a gigabit per second. Divided by 8 (bits to bytes) = 125 MB/s. A 1 Gbps line downloads 1 GB in 8 seconds (theoretical).
- Cloud storage. AWS S3 charges per GB (decimal). 1 TB = 1000 GB for billing.
- Computer RAM. "16 GB RAM" advertised is actually 16 GiB. Marketing sticks with decimal, but physically the chips come in powers of 2.
- Migrating files between disks. "Will it fit?" Pay attention whether both report in GB or one in GB and the other in GiB.
- Education. See exactly why your disk "lies" about its capacity. It's not lying, it's a convention difference.
Questions and answers
Because there are two different systems. Decimal (TB) = 10^12 bytes = 1 trillion. Binary (TiB) = 2^40 bytes = 1.099 trillion. Disk makers use decimal (bigger marketing number). RAM, Windows, some systems use binary.